1. Field of the Invention
The present invention relates to a high-precision optical adaptor for an endoscope that is freely detachably attached to the distal part of an endoscope.
2. Description of the Related Art
In recent years, endoscopes having elongated insertion units inserted into a body cavity for observing or treating an intracavitary organ using, if necessary, a treatment appliance passed through a treatment appliance channel therein, have been widely employed. Endoscopes for industrial use have been widely used to observe or inspect the interior of a boiler, a turbine, an engine, a chemical plant, or the like for flaws, corrosion, or the like.
The endoscopes include an electronic endoscope, having an imaging device, such as a CCD in the distal part of an insertion unit thereof. The electronic endoscope uses a display means, such as a monitor, to display an optical image of a region examined, which is projected on the imaging device, and thus enables observation of the region.
A proposed type of electronic endoscope is such that an optical adaptor having a plurality of identical or different objective optical systems is freely detachably attached to the distal part of an endoscope. A plurality of optical images of a region to be examined are concurrently projected on an imaging device incorporated in an insertion unit via the optical adaptor.
For improving the optical characteristics of the optical adaptor, for example, Japanese Unexamined Patent Publication No. 11-109257 entitled xe2x80x9cImaging optical system of an endoscopexe2x80x9d disclosed an optical adaptor. An optical adaptor is composed of a plurality of identical or different objective optical systems, and one relay optical system for transmitting a plurality of images formed by the objective optical systems.
In the imaging optical system of an endoscope, an adaptor having objective optical systems, which share the same specifications, arranged therein is attached in order, not only merely to perform an endoscopic examination, but also to measure an object according to a known trigonometric survey method. For measurement, images formed by two objective optical systems are projected onto one CCD. Measurement can be achieved highly precisely because the adaptor is designed so that the focal distance of a front group of lenses in an image transmission optical system can be varied. A large distance can therefore be preserved between objective optical systems.
By contrast, Japanese Unexamined Patent Publication No. 9-101465 disclosed the practical structure of a binocular optical adaptor as an optical adaptor for an endoscope. The binocular optical adaptor has two optical systems and transmits optical images to an imaging device, such as a CCD, located in the distal part of an insertion unit.
However, in the optical adaptor for an endoscope described in the Japanese Unexamined Patent Publication No. 9-101465, the distal part of an endoscope is located perpendicularly to an optical axis near the proximal end surface of the adaptor. The distal endoscope part has an imaging device stowage portion in which an imaging device, such as a CCD, is stowed. The imaging device requires a large stowage space compared with a system of lenses in an optical system. The outer diameter of the distal endoscope part must be large enough to preserve a space required for the imaging device stowage portion and a space required for the attaching/detaching structure of the optical adaptor. This poses a problem in that the outer diameter of the optical adaptor attachable to the distal endoscope part must be large.
Assuming that the optical adaptor disclosed in the Japanese Unexamined Patent Publication No. 11-109257 entitled xe2x80x9cImaging optical system of an endoscopexe2x80x9d is adapted to an actual product, since a plurality of identical or different optical systems juxtaposed in an axial direction and one relay optical system located in tandem behind the optical systems are arranged in one adaptor, the structure of the adaptor becomes complex. Assembling therefore is difficult and introduces uncertainty. Consequently, specifications differ from product to product. When a distance between the objective optical systems and relay optical system differ from a specified distance, an observable depth is affected seriously.
Furthermore, when a side-view type adaptor is used to measure an object, images formed by two objective optical systems project at a 90xc2x0 angle into the CCD using one prism. The object is then measured according to a known trigonometric survey method. For this reason, a parallax stemming from two optical axes cannot be physically increased to be equal to or larger than the diameter of the insertion unit. For highly precise measurement, the objective optical systems must be distanced well apart from each other in order to ensure a large parallax. This increases the diameter of the insertion unit.
An object of the present invention is to provide an optical adaptor for an endoscope enabling highly precise assembling despite a complex structure.
Another object of the present invention is to provide an optical adaptor for an endoscope enabling highly precise measurement of an object.
Still another object of the present invention is to provide an optical adaptor for an endoscope with a small outer diameter.
Briefly, according to the present invention, an optical adaptor for an endoscope enabling optically highly precise arrangement comprises a first frame member, a second fame member, and a distance restriction member. The first frame member is the distal part of the optical adaptor, and has a plurality of objective optical systems stowed and held therein. The second frame member is located behind the plurality of objective optical systems, and has a relay optical system stowed and held therein. The relay optical system transmits optical images formed by the objective optical systems, and cooperates with an imaging optical system of an endoscope located ahead of an imaging device to form an image transmission optical system. The distance restriction member is interposed between the first frame member and second frame member, and restricts the distance between the members to a predetermined value.